Towards a Middle Pleistocene terrestrial climate reconstruction based on herpetofaunal assemblages from the Iberian Peninsula: State of the art and perspectives

Abstract

31The pattern of the varying climatic conditions in southern Europe over the last million 32 years is well known from isotope studies on deep-ocean sediment cores and the long 33 pollen records that have been produced for lacustrine and marine sedimentary sequences 34 from Greece, Italy and the Iberian margin. However, although relative glacial and 35 interglacial intensities are well studied, there are still few proxies that permit 36 quantitative terrestrial temperature and precipitation reconstruction. In this context, 37 fauna-based climate reconstructions based on evidence preserved in archaeological or 38 palaeontological sites are of great interest, even if they only document short windows of 39 that climate variability, because (a) they provide a range of temperature and 40 precipitation estimates that are understandable in comparison with present climate; (b) 41 they may allow the testing of predicted temperature changes under scenarios of future 42 climate change; and (c) quantitative temperature and precipitation estimates for past 43 glacials and interglacials for specific regions/latitudes can help to understand their 44 effects on flora, fauna and hominids, as they are directly associated with those cultural 45 and/or biological events. Moreover such reconstructions can bring further arguments to 46 the discussion about important climatic events like the Mid-Bruhnes Event, a climatic 47 transition between moderate warmths and greater warmths during interglacials. In this 48 paper we review a decade of amphibian-and reptile-based climate reconstructions 49 carried out for the Iberian Peninsula using the Mutual Ecogeographic Range method in 50 3 order to present a regional synthesis from MIS 22 to MIS 6, discuss the climate pattern 51 in relation to the Mid-Bruhnes Event and the thermal amplitude suggested by these 52 estimates and finally to identify the chronological gaps that have still to be investigated. 53 54

Early Pleistocene conifer macrofossils from Happisburgh, Norfolk, UK, and their environmental implications for early hominin occupation

“…Compared with the present-day mean summer (+18.4 °C) and winter (+2.6 °C) temperatures this indicates that MIS 21 summer palaeotemperatures could have been similar to that of today or as much as 4.1 °C warmer or 3.4 °C cooler, and mean winter temperatures could have been similar to that of today or as much as 4.9 °C warmer or 3.6 °C cooler. In summary, Blain et al (2018) interpret their results as indicating a temperate Mediterranean palaeoclimate with both summers and winters similar to or somewhat warmer than today; our interpretation of their results, on the other hand, would allow the additional possibility that summers and /or winters may have been significantly cooler. This is not to say that Blain et al (2018) are wrong, however; a recent publication by Altolaguirre et al (2018) has used an MPC approach (although they do not name it as such) to compare results from Blain et al (2009) with new ones based on pollen and leaf assemblages using the Coexistence Approach (Mosbrugger and Utescher, 1997;Utescher et al, 2014;Alcalde-Olivares et al, 2004).…”

“…In summary, Blain et al (2018) interpret their results as indicating a temperate Mediterranean palaeoclimate with both summers and winters similar to or somewhat warmer than today; our interpretation of their results, on the other hand, would allow the additional possibility that summers and /or winters may have been significantly cooler. This is not to say that Blain et al (2018) are wrong, however; a recent publication by Altolaguirre et al (2018) has used an MPC approach (although they do not name it as such) to compare results from Blain et al (2009) with new ones based on pollen and leaf assemblages using the Coexistence Approach (Mosbrugger and Utescher, 1997;Utescher et al, 2014;Alcalde-Olivares et al, 2004). They find that the two proxy methods give consistent results, thus validating them, but stop short of using them to determine narrower "mutual mutual" ranges in the way that we have done for HSB3.…”

“…It is interesting to compare the HSB3 results with palaeotemperature reconstructions obtained with the herpetile Mutual Ecogeographic Range (MER) method by Blain et al (2018) for the MIS 21 Gran Dolina (TD6) human occupation site in northern Spain. Their results (Blain et al, 2018: Table 2) for mean summer temperature vary from +18.5(±2.1) °C to +20.3(±1.2) °C, from which they calculate differences from present-day temperature of +0.1 and +1.9 °C respectively (i.e. very similar or, at most, less than 2 °C warmer).…”

“…very similar or, at most, less than 2 °C warmer). These, however are mean values, calculated from reconstructed ranges that are not shown by Blain et al (2018) but were originally provided (as minima and maxima), in addition to means and standard deviations, by Blain et al (2009). The overall ranges for the combined TD6 levels are +15.0 to +22.5 °C (summer) and -1.0 to +7.5 ° C (winter).…”

“…It is beyond the scope of the present paper to assess whether the apparent precision (calculation of means to one decimal place) of the MER method used by Blain et al (2018) is indicative of greater accuracy, but in MCR methods (including our own new conifer MCR method) we work to a precision of one whole degree (no decimal places) and consider it questionable whether the mean of the upper and lower values of a range has a greater probability (than any other value within that range) of being correct (Buckland, 2007;Horne et al, 2012a). Comparability of sites is also problematic due to chronological uncertainties; since HSB3 is assigned to either MIS 25 or MIS 21 and most likely represents the second half of an interglacial (Parfitt et al, 2010) it can only tentatively be regarded as approximately equivalent to Gran Dolina TD6, which is assigned to MIS 21 and held to include the interglacial optimum (Blain et al, 2018).…”